The goal of this project is to characterize the clinical features and the immunology, and to attempt therapy of severe chronic illnesses associated with EBV infection. To date we have studied in detail approximately twelve such individuals ranging in age from 4 to 36. While this study is being done under a new project number, this work was done previously as part of another broader research project. In the course of the study, we have witnessed a range of illness that could be attributed with variable certainty to Epstein Barr virus. Noteworthy observations included markedly elevated virus specific antibodies, the detection in several patients of EBV proteins or RNA in their tissues. The study is continuing with a major emphasis on the investigations of the immunopathogenesis of the disorder. Whatever its cause, it has been sufficiently severe to lead to the death of 5 of our patients thus far and a 6th one has currently progressed to a life threatening monoclonal lymphoma.